The present invention relates to a method of preparing high alkalinity sulfurized alkylphenates of alkaline earth metals useful as detergent-dispersant additives for lubricating oils, the additives prepared by this method, and lubricating oils containing these additives.
It is known in the art to prepare high alkalinity sulfurized calcium alkylphenates by sulfurizing and neutralizing dodecylphenol with sulfur and lime in the presence of an oil and a glycol (or by neutralizing a sulfurized alkylphenol with lime in the presence of an oil and a glycol), carbonating the resultant medium, distilling off the glycol, and filtering the oily solution containing the sulfurized calcium alkylphenate.
Because the glycol acts both as a dilution solvent and as a dispersant of the calcium carbonate in the medium, the prior art method has the drawback of requiring a large quantity of glycol, 50% of which remains in the final product and is detrimental to the engines with which the additive is used. Other drawbacks of the prior art include the high viscosity of the reaction medium, especially at the end of the sulfurization-neutralization step, the undesirable oxidation-reduction reactions that take place between the sulfur and the glycol, the results of which are detrimental to the performance of the end product (in particular the anti-oxidant properties of the end product), and the production of high quantities of H.sub.2 S due to the large excess of sulfur necessary to sulfurize the alkylphenol.